A biodegradable protein fiber Antheraea assama silk (SH) was modified by using graft co-polymerization technique with methyl methacrylate (MMA; vinyl monomer) and cerric ammonium sulfate (Ce-IV). The grafting process was dependent on MMA, Ce-IV, time factors, temperatures and other properties of the fibroin composites. The possible mechanism of the SHMMA composite was explained by free radical co-polymerization, and the thermal properties were characterized by thermogravimetric analysis (TGA), differential thermogravimetry (DTG), differential thermal analysis (DTA), and differential scanning calorimetry (DSC). The kinetic parameters were also studied using the Coats and Redfern method with FORTRAN 77 computer programming and evaluating the activation energy. The structural changes of SHMMA, changes of the crystalline and amorphous characteristics after chemical process with MMA-Ce-IV initiator, were discussed in relation to the weight gain and X-ray diffraction curves. This study shows that silk fibroin composites modified by graft co-polymerization have improved thermal stability and chemical stability, which improve the drawbacks and make the silk fibroin a promising material in constructing textiles.